An antenna device, including a case assembly, a first waveguide assembly, and a second waveguide assembly, is provided. A cavity is defined by an interior of the case assembly, and a first side of the case assembly has a slot penetrating the case assembly. At least part of the first waveguide assembly is located within the cavity and is connected to the first side. A projection of the first waveguide assembly to the first side is symmetrically located on two sides of the slot. The second waveguide assembly is located outside the case assembly, is close to the first side, and is connected to the slot. The second waveguide assembly is suitable for transmitting an antenna signal to the cavity through the slot and the first waveguide assembly. The antenna signal resonates in the cavity and radiates outward from a second side of the cavity opposite to the first side.